1. Field of the Invention
The present invention relates to an injector that performs injection supply of high pressure fuel to a combustion chamber of an internal combustion engine.
2. Description of Related Art
An injector using an electromagnetic valve as an actuator is commonly used. In order to realize a large flow rate and high response, an injector using a piezoelectric actuator with a large generative force and high response is proposed. For example, an injector described in Patent document 1 (International Publication No. 2005/075811) has a piezoelectric actuator 100 that makes a displacement when voltage is applied thereto, a pressurizing piston 110 driven by the piezoelectric actuator 100, an outer sleeve 120 for slidably holding an outer periphery of the pressurizing piston 110, a pressure chamber 130, internal pressure (hydraulic pressure) of which increases/decreases according to movement of the pressurizing piston 110, a needle 160 that is slidably held inside a valve body 140 and that has a function to open/close an injection hole 150 and the like as shown in FIG. 6.
The pressure chamber 130 is fluid-tightly defined by the pressurizing piston 110, the outer sleeve 120, the needle 160 and the valve body 140. If the voltage is applied to the piezoelectric actuator 100 and the pressurizing piston 110 is depressed downward in the drawing, the volume of the pressure chamber 130 decreases and the internal pressure rises.
The internal pressure of the pressure chamber 130 acts on a pressure receiving face 161 formed on the needle 160 to function as a valve opening force for biasing the needle 160 in a valve opening direction (upward direction in the drawing). If the valve opening force exceeds a valve closing force (reaction force of the spring 170 and the like) biasing the needle 160 in a valve closing direction, the needle 160 lifts and opens the injection hole 150. Thus, the high pressure fuel supplied to an inside of the valve body 140 is injected into a combustion chamber 180 of the engine from the injection hole 150.
In order to efficiently generate the hydraulic pressure (the internal pressure of the pressure chamber 130) for driving the needle 160, fuel leak from the pressure chamber 130 should be inhibited and the volume of the pressure chamber 130 should be made small.
In the injector described in Patent document 1, the pressure chamber 130 includes a space A (a shade area in FIG. 6) formed between the pressure receiving face 161 of the needle 160 and an end face of the valve body 140. Therefore, it is difficult to make the pressure chamber 130 compact. In order to inhibit the fuel leak, strict management of a clearance at a needle sliding section S shown in FIG. 6 and precise processing are required. Accordingly, a cost can be increased.